The present invention relates to the coagglomeration of random vinyl substituted aromatic/C4-C6 conjugated diolefin polymers with sulfur. Said coagglomerate is storage stable and easily blended with asphalt under a variety of mixing conditions. Further, polymer/asphalt blends prepared with the sulfur coagglomerated polymers show improved storage stability against phase separation.
Sulfur vulcanization of StyrenelButadiene/Styrene block copolymers and Styrene/Butadiene Rubber (SBR) to improve the mechanical properties of polymer/asphalt admixtures is known to those skilled in the art. Specifically, U.S. Pat. No. 3,803,066 discloses a modified bitumen prepared by blending a powder or latex of rubber (natural or synthetic) into the bitumen at 125-160xc2x0 and adding sulfur and a vulcanization accelerator (e.g. organic peroxide) to this mixture in a ratio of sulfur to rubber of 0.3 to 0.9. Said modified bitumen is homogeneous and ductile at low temperatures. U.S. Pat. No. 3,634,293 discloses compositions containing bitumen, olefin polymers (e.g ethylene acrylate), a base (e.g. metal salt of an oxide, hydroxide, sulfide, carbonate or silicate) and sulfur. The order of addition can be bitumen plus polymer followed by sulfur addition or all together. Said composition is said to be homogeneous and elastic. U.S. Pat. No. 3,992,340 discloses vulcanized molding compositions comprising bitumen and olefin polymers and sulfur. These molding compounds have a 2:1 to 1:1 weight ratio of bitumen to olefin polymer. Various orders of addition of ingredients were disclosed including (i) bitumen plus sulfur and a vulcanization accelerator, these are then added to the olefin (e.g. styrene/butadiene) polymer (ii) bitumen olefin polymer and sulfur mixed all together, and cured by the vulcanization accelerator addition, (iii) mixing bitumen, olefin polymer, sulfur, a vulcanization accelerator all together and (iv) prepare a homogeneous mixture of an olefin polymer, sulfur and a vulcanization accelerator, followed by mixing the homogeneous mixture with bitumen.
U.S. Pat. No. 4,130,516 discloses the addition of 3-7% sulfur into asphalt to increase ductility. A small amount (0.5-1.5%) of SOLPRENE(copyright) 1206 (a linear random styrene/butadiene copolymer) is added to further increase ductility.
U.S. Pat. No. 4,412,019 discloses the use of a hydrogenated styrenelbutadiene rubber (e.g Solprene 512xe2x80x94a substantially linear butadiene/styrene block copolymer coupled with epoxidized soy bean oil) with sulfur for improving the temperature stability of asphalt. The hydrogenated styrene/butadiene rubber is used at a level of 5-20% and the sulfur is used at a level of 1-40% sulfur in the asphalt. The polymer has a molecular weight of 70,000.
U.S. Pat. Nos. 4,145,322, 5,314,935, 5,371,121, all disclose bitumen/polymer compositions wherein bitumen and di or tri block copolymers are blended together, and then the sulfur, or sulfur plus vulcanization accelerator, is added to the bitumen/polymer blend.
U.S. Pat. No. 4,242,246 discloses a process for the preparation of bituminous compositions making use of a mother solution containing styrene/butadiene block co-polymers and sulfur in a petroleum solvent. The polymers are block copolymers of styrene and butadiene of molecular weight 30,000 to 300,000, preferably between 70,000 and 200,000. Said styrene/butadiene block co-polymer is premixed with sulfur (2 to 6% by weight to the polymer) into a petrolerm solvent. The styrene/butadiene block polymerisulfur/solvent mixture is blended into the asphalt.
U.S. Pat. No. 4,554,313 discloses a process for preparing bitumen-polymer compositions comprising the use of organic sulfur compounds, such as ditertiododecyl or dinonyl pentasulphide. The polymers are random or block copolymers of styrene and butadiene of molecular weight 30,000 to 300,000, preferably between 70,000 and 200,000. The sulfur compound and co-polymer are dissolved into a hydrocarbon oil, and then added to the asphalt.
U.S. Pat. No. 4,576,648 discloses cationic emulsions of bituminous binders of the bitumen type comprising cationic asphalt emulsions prepared using the polymer modified asphalt disclosed in U.S. Pat. No. 4,554,313.
U.S. Pat. No. 5, 672,642 discloses a process for preparing storage stable asphalt/polymer blends prepared by contacting elemental sulfur with asphalt to form a blend. Said elemental sulfur/asphalt blend is added to the polymer. The preferred polymers are diene block copolymers such as styrene/butadiene/styrene and styrene/isoprene/styrene.
Additionally, styrenetbutadiene rubber latex containing sulfur and/or a vulcanization accelerator is commercially available as BUTONAL(copyright) NX 1106x and ULTRAPAVE(copyright) 5061. The sulfur and vulcanization accelerator were simply added to the latex.
Applicants have discovered that an aqueous sulfur dispersion, with or without a vulcanization accelerator, can be co-agglomerated with the SBR base latex for the preparation of the high solids sulfur co-agglomerated SBR latex. Surprisingly, the sulfur co-agglomerated SBR latex is easier to mix with the asphalt and either reduces or totally eliminates separation of the polymer rich layer during storage at elevated temperature (e.g. 160xc2x0 C. to 180xc2x0 C. for 2 to 3 days). Further, if separation occurs, it is easily re-mixed with gentle agitation. Thus, the polymer-asphalt admixture prepared with the sulfur co-agglomerated SBR latex maintains homogeneity. Further, Applicants"" method requires no petroleum solvents and less sulfur is required.
Finally, since the SBR latex polymer/sulfur agglomerate is storage stable, it is easily blended with the asphalt on the job site, alleviating the compatibility problems associated with polymer modified asphalts.
DEFINITIONS AND USAGES OF TERMS
The term xe2x80x9crandom copolymerxe2x80x9d, as used herein, means a polymer in which the monomeric units comprising said polymer are randomly arranged.
The term xe2x80x9cblock copolymerxe2x80x9d, as used herein, means a polymer in which the monomeric units comprising said polymer are arranged in blocks, e.g [styrene-butadiene-styrene]-[styrene-butadiene-styrene].
The term, xe2x80x9cagglomerationxe2x80x9d and xe2x80x9cco-agglomeration,xe2x80x9d as used herein, means processes producing a latex having a broad particle size distribution, which is essential to achieve a low enough viscosity at this high total solids. Detailed descriptions of the various agglomeration processes can be found in E. W. Madge, xe2x80x9cLatex Foam Rubber, Chapter 14, Methods of Manufacture of General Purpose Synthetic Latex For Foam Rubber Productionxe2x80x9d, Maclaren and Sons Ltd., London, 1962.
The term xe2x80x9clatex formxe2x80x9d, as used herein, means stable polymer emulsions.
The term xe2x80x9cmPas,xe2x80x9d as used herein, means milli Pascal second. It is used to express viscosity.
The terms xe2x80x9casphaltxe2x80x9d and xe2x80x9cbitumenxe2x80x9d, as used herein, can be used interchangably.
All weights are weight % unless otherwise indicated.
The present invention relates to a process for preparing random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer/sulfur coagglomerates comprising the steps of:
(a) blending said random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and an aqueous dispersion of sulfur;
(b) agglomerating the blended random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and sulfur formed in step (a) to form a coagglomerate in latex form.
The present invention also relates to a method for improving the homogeneity of random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer/asphalt admixtures:
(a) blending said random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and an aqueous dispersion of sulfur.
(b) agglomerating the blended random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and sulfur formed in step (a) to form a coagglomerate in latex form.
(c) Mixing of said coagglomerate formed in step (b) with the asphalt at temperature between 100xc2x0 C. and 160xc2x0 C.
Further, the vinyl substituted aromatic, e.g. the styrene, component of the latex polymer may be reduced or omitted. Thus, the C4-C6 conjugated diolefin homopolymer, polybutadiene for example, may be co-agglomerated with the sulfur without the vinyl substituted aromatic (e.g. styrene) polymer. The vinyl substituted aromatic (e.g.styrene) component of the latex polymer which is blended with the sulfur dispersion to form a co-agglomerate can be at a level of 0-35%.
The present invention relates to a process for preparing random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer/sulfur coagglomerates comprising the steps of.
(a) blending said random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and an aqueous dispersion of sulfur;
(b) agglomerating the blended random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and sulfur formed in step (a) to form a coagglomerate in latex form.
The present invention also relates to a method for improving the homogeneity of random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer/asphalt admixtures of:
(a) blending said random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and an aqueous dispersion of sulfur;
(b) agglomerating the blended random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer and sulfur formed in step (a) to form a coagglomerate in latex form.
(c) Mixing of said coagglomerate formed in step (b) with the asphalt at temperature between 100xc2x0 C. and 160xc2x0 C.
Further, the random vinyl substituted aromatic, e.g. the styrene, component of the latex polymer may be reduced or omitted. Thus, the C4-C6 conjugated diolefin homopolymer, polybutadiene for example, may be co-agglomerated with the sulfur without the vinyl substituted aromatic (e.g. styrene) polymer. The vinyl substituted aromatic (e.g.styrene) component of the latex polymer which is blended with the sulfur dispersion to form a co-agglomerate can be at a level of 0-35%.
The latex polymer-sulfur coagglomerate prepared in step (b) is easy to mix with the asphalt, and either reduces or eliminates formation of the polymer rich layer on the asphalt-polymer admixture surface during storage at elevated temperature 160xc2x0 C. to 180xc2x0 C.) for a prolonged period (2 to 3 days).
Further, the polymer rich layer, if formed, is easily re-mixed in with gentle agitation, thus, the polymer-asphalt admixture prepared in step (c) with the latex-sulfur coagglomerate maintains homogeneous mixture with or without a low shear mixing during storage.
The Practice of the Present Invention
The coagglomeration of the sulfur dispersion and the random vinyl substituted aromatic/C4-C6 conjugated diolefin latex polymer is key to the invention. Without intending to be limited, the coagglomeration can be carried out in a variety of ways.
The sulfur dispersion is blended with the random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer at levels 0.5 to 10%, more preferably 1-6%, most preferably 2-3%. After blending with the random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer the coagglomeration process begins.
Several coagglomeration processes, such as freeze, pressure and chemical coagglomeration processes have been commercially utilized. Detailed description of these coagglomeration processes as well as the production of the SBR latex can be found in E. W. Madge, xe2x80x9cLatex Foam Rubber, Chapter 14, Methods of Manufacture of General Purpose Synthetic Latex For Foam Rubber Productionxe2x80x9d, Maclaren and Sons Ltd., London, 1962. Basically, high solids SBR latex is produced by the coagglomeration process followed by water removal to produce the latex dispersion of 68-72% total solids. The agglomeration process produces a latex dispersion having very broad particle size distribution of below 100 nm to above a few micrometers in diameter.
The coagglomerate is in the anionic form. Said coagglomerate can be converted to the cationic form by the addition of cationic surfactants, including, but not limited to, Redicote(copyright) E-5, Redicoate(copyright) E-11, Redicote(copyright) E-53, Redicote(copyright) E-606, Redicote(copyright) 5127 (proprietary cationic amines) available from Akzo Nobel. Adogen(copyright) 477HG (tallow pentamethyl propane diammonium-chloride, from Witco), Indulin(copyright) W-1, Indulin(copyright) W-5, Indulin(copyright) SBT, Indulin(copyright) MQK (from Westvaco) are also suitable cationic surfactants. Other cationic surfactants suitable in the practice of the present invention are described in: U.S. Pat. No. 4,576,648, col 3, line 57 to col 4, line 28; U.S. Pat. No. 5,374,672 col 7, line 43 to cot 8, line 36; U.S. Pat. No. 5,382,612 col 8, line 62 to col 9, line 53, incorporated by reference herein.
The random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer/sulfur co-agglomerate is used at levels of 1-10%, preferably 2-5% in the asphalt. The final of sulfur level in the asphalt is 0.005-1.0%.
The Random Vinyl Substituted Aromatic/C4-C6 Conjugated Diolefin Polymer Suitable for Use in The Present Invention
The random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer suitable for use in the present invention comprises from about 65 to 100% by weight of a least one conjugated C4-C6 diolefin and from about 0%-35% by weight of a vinyl substituted aromatic. Styrene/butadiene rubber latex (SBR) is the preferred random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer. Preferred stryenel butadiene rubber latex is available from BASF as BUTOFAN(copyright) NS 103.
The Asphalt Suitable for Use in The Present Invention
The asphalt suitable for use in the present invention is described in U.S. Pat. No. 5,672,642, column 1, lines 60-67 and column 2, lines 1-25, incorporated by reference herein.
The Sulfur Useful in the Practice of the Present Invention
Sulfur useful in the practice of the present invention is described in: U.S. Pat. No. 5,618,862 col 3, line 53 to 57; U.S. Pat. No. 5,382,612 col 5, line 54-59; U.S. Pat. No. 5,314,935 col 5, line 66 to col 6, line 2; U.S. Pat. No. 4,412,019 col 2, line 51-56; U.S. Pat. No. 4,242,246 col 2, line 65 to col 3 line 4, incorporated by reference herein.
Elemental sulfur as a dispersion is preferred. BOSTEX(copyright) 410 (68% elemental sulfur as a dispersion) available from Akron Dispersions is most preferred. The sulfur dispersion is blended with the random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer at levels 0.5 to 10%, more preferably 1-6%, most preferably 1-3%. After blending with the random vinyl substituted aromatic/C4-C6 conjugated diolefin polymer the coagglomeration process begins.
Vulcanization Accelerators Useful in-the Practice of the Present Invention
Vulcanization accelerators are optional. However, if used, suitable vulcanization accelerators are disclosed in; U.S. Pat. No. 5,618,862, col 3, line 34-52 and col 3, line 58 to col 5, line 28; U.S. Pat. No. 5,684,091, col 1, line 61 to col 4, line 36; U.S. Pat. No. 5,382,612 col 5, line 32 to col 8, line 33; U.S. Pat. No.5,314,935 col 5, line 47 to col 8, line 40 and incorporated by reference herein;
Further xe2x80x9cTHE VANDERBILT RUBBER HANDBOOKxe2x80x9d, published by R. T. Vanderbilt Company, Inc. Norwalk, Conn., Thirteenth Edition (1990), pages 12-16 contains a general description of sulfur vulcanization, and pages 296-330 describe suitable vulcanization accelerators.
Two preferred vulcanization accelerators are BOSTEX(copyright) 533B (50% active dispersion of 2-mercaptobenzothiazole) and Bostex(copyright) 224 (50% active dispersion of dipentyl-methylene thiuramsulfide).